The present invention relates to a method of making an extremely fine-grained titanium-based carbonitride alloy.
Titanium-based carbonitrides, often named cermets, are known for having considerably better wear resistance but at the same time inferior toughness behavior than conventional, i.e., WC-Co based, cemented carbide at the same content of hard constituents. Such carbonitride alloys are therefore used most often for extreme finishing at high speed under stable conditions at which they generate very fine surfaces on the work piece. At the same time, they maintain their tolerances for a long time because of their superior wear resistance.
One reason for the better wear resistance of titanium-based hard materials compared to tungsten-based materials is that the titanium hard constituents have much better chemical stability than tungsten hard constituents. The very much active diffusional wear mechanism at high temperature has thus essentially a lower effect for titanium-based hard materials. Another effect of the good chemical stability is a decreased tendency to clad the work-piece material onto the tool.
Methods used to improve the toughness behavior are to increase the content of binder phase which leads to impaired high temperature properties and decreased wear resistance. Alternatively, an improved toughness behavior at maintained binder phase content can be obtained by increasing the grain size.
The established experience within the powder metallurgy art, particularly within cemented carbide technique and industry, is that a reduction of the grain size at a constant binder phase content leads to increased hardness and decreased toughness. The increasing hardness and the decreasing toughness have been related to the decrease of the free mean path length in the binder phase. This is well-known to those skilled in the art and it is therefore logical to increase the grain size in order to increase the toughness.